1. Field of the Invention
The present invention relates to a locking unit for a telescopic system of a hydraulically actuated telescopic jib of a crane having a jib box frame and a plurality of telecopic sections guided one inside another and moveable from a starting section position to an extended position, and to a telescopic jib.
2. Description of the Related Art
EP 0 661 234 A1 and counterpart U.S. Pat. No. 5,628,416 discloses a crane with a telescopic jib which has at least one box frame in which a plurality of telescopic sections of the jib are arranged, these sections being extendable from a starting position into, in each case, one extended position. In the starting position, the individual sections which are guided inside one another are secured to one another and/or to the box frame of the jib by means of a locking bolt. The extension and retraction of the individual sections is in each case effected by a single-stage piston-cylinder unit, which is releasably coupled to the section which is to be displaced by means of a locking unit. This coupling is effected by means of two driver bolts of the locking unit, which can be introduced in a positively locking manner into corresponding locking openings in the section which is to be moved. The driver bolts are held in the locking position by spring preloading and can be pulled out of the locking position, in order to be uncoupled in each case from the moved section of the jib, by means of a mechanism which is actuated by a hydraulic cylinder of the locking unit. The locking unit is equipped with a coupling device which can move relative to the locking unit and by means of which the respective locking bolt can be gripped and pulled out of the locking opening. The locking bolt, like the driver bolt, is held in the locking opening by spring preloading and is unlocked counter to the spring force by the coupling device. A hydraulic drive by a piston-cylinder unit is provided for the unlocking movement of the coupling device. In this known crane, the free end of the piston rod of the single-stage piston-cylinder unit which is provided for movement of the individual sections is attached to the lower end (with respect to the working position) of the telescopic jib, while the locking unit is attached to the extendable cylinder housing (telescopic cylinder) of the piston-cylinder unit.
A telescopic system with a single-stage telescopic cylinder unit which functions in a similar way is known from EP 0 943 580 A2 and its counterpart U.S. Pat. No. 6,216,895. This system, however, does not use a single locking bolt to secure the individual sections to one another, but rather a pair of locking bolts which in each case engage in locking openings arranged in the side faces of the individual sections. The locking bolts lie opposite one another with respect to the longitudinal axis of the jib. To actuate the locking bolts, which are likewise held in the locking position under spring preloading, there is a separate hydraulic piston/cylinder unit, which acts on the locking bolts via a lever system.
DE 198 24 671 A1 and its counterpart U.S. Pat. No. 6,189,712 discloses a telescopic crane, the sections of which can be moved telescopically by a single hydraulic piston-cylinder system. In this case, the displaceable part of the piston-cylinder system, i.e. either the piston rod or the cylinder housing, is equipped with two locking units, one of which is arranged at the upper end of the displaceable part and the other of which is arranged at the lower end of the displaceable part. This makes it possible to considerably shorten the length of the piston-cylinder system with respect to the required length in the solution described in EP 0 661 234 B1 or EP 0 943 580 A2, for example to shorten this length by half. However, in this case the extension of a section is carried out in two steps; in the first step, the lower locking unit is used, and in the second step the upper locking unit is used. The reverse is true when retracting a section. In this known solution, the locking unit once again has two driver bolts which lie opposite one another and is designed to actuate an individual locking bolt for each section. In this case, the driver bolts and the locking bolt are actuated via a common drive of a hydraulic piston-cylinder system on the locking unit. This piston-cylinder system acts, via a cam-controlled mechanism, to convert the linear movement on the driver bolts and the locking bolt in such a manner that the locking bolt can only be unlocked when the two driver bolts have been introduced into the respective driver openings of the section which is to be moved. Conversely, the driver bolts can only be pulled out of the driver openings of the section in question when the locking bolt is in its locked position. This ensures that there can be no uncontrolled extension or retraction of a section without the guidance provided by the hydraulic telescopic piston-cylinder unit.
These known solutions have the drawback that, to actuate the locking units, which are fixedly connected to the movable part of the telescopic piston-cylinder system, it is necessary to provide hydraulic feedlines leading to this movable part. This requires a considerable construction and assembly outlay.
It is an object of the present invention to reduce the outlay involved in actuating a locking unit of the generic type without impairing its operational reliability.
In accordance with the invention, a locking unit for a hydraulically actuated telescopic job of a crane having a jib box frame and a plurality of telescopic sections guided one section inside another and each moveable along a jib axis from a starting position into at least one extended position is provided with an actuating means for displacing the telescopic sections, the locking unit being fixedly connected to the actuating means and including at least one driver bolt. A drive is operable to displace the driver bolt along said axis for introducing said driver bolt into a driver bolt opening in the telescopic section. A coupling device is arranged with the locking unit and the drive is operable to move the coupling device relative to the locking unit. Each section is provided with an axially displaceable locking bolt receptive in a locking opening for fixing a section in a locking position such that it, (the section) cannot be displaced into one of another section or the box frame. The coupling device is operable to grip and pull the at least one locking bolt out of an associated locking opening. The drive is arranged fixedly on the box frame, and a mechanical drive is connected between the drive and the locking unit.
The essential distinguishing feature of the present invention is that the drive for moving a driver bolt (two driver bolts are preferably provided) and for moving the coupling device in order to displace a locking bolt (two locking bolts are preferably provided) is arranged fixedly on the box frame of the jib and that there is a mechanical drive connection between this drive and the locking unit. Therefore, there are deliberately no hydraulics acting in the locking unit, and consequently the locking unit also does not have to be provided with hydraulic feed lines and outlet lines. It is also unnecessary to provide an electro-mechanical drive in the locking unit, which would require corresponding electrical connection lines to the locking unit. To drive the locking unit, it is preferable to provide a rotary motor drive which is arranged in the region of the lower end of the box frame, the mechanical drive connection comprising a profiled rod, which is arranged substantially parallel to the longitudinal axis of the telescopic jib, for torque transmission. In the locking unit there is a mechanism which converts the rotary movement of the profiled rod into translational movements for the driver bolt(s) and the locking bolt(s). In this case, the profiled rod may be guided slidably in a drive wheel, in particular in a toothed wheel, which is mounted rotatably and in a fixed position on the locking unit. The rotary movement can be converted into the required translational movement for example by a rack drive, on which the drive wheel acts, or a crank drive or a slotted-guide control means.
Instead of a rotary drive movement, it is also possible for the drive, which is arranged outside the locking unit, to execute a sliding movement, which can be transmitted to the locking unit by a connecting rod. During the telescopic movement of a section, this connecting rod may be guided in a sliding manner in the locking unit and, when the desired locking position of the section is reached, can be fixedly connected to a coupling element of the locking unit in order to transmit linear movements. For this purpose, it is advantageously possible to provide a coupling fixture which can be engaged in a positively locking manner, in particular a coupling fixture which is designed as a driver projection and can be engaged by a rotary movement of the connecting rod. Alternatively, the connecting rod may also be of tubular design and the coupling fixture may be in the form of a spreading fixture which, for example, can be actuated mechanically by an actuating rod in the connecting rod, from the lower end of the box frame of the telescopic jib. A spreading fixture of this type could also be activated and deactivated by a rotary movement of the actuating rod.
If, by way of example, two driver bolts are provided, it is advantageous for these bolts to be arranged on opposite sides with respect to the longitudinal axis of the jib. Accordingly, when using two locking bolts these locking bolts should also be arranged on opposite sides of the telescopic jib, preferably in the region of the side faces of the respective section.
To ensure that the drive bolts and the locking bolts are held securely in their locking position when they are not actuated by the locking unit, it is preferable for the locking bolts and driver bolts to be fixed in engagement in the locking opening or driver opening by spring preloading.
A telescopic jib according to the invention has at least one, and preferably two, locking units of the type described above, which are fixedly connected to the actuating means which effects the displacement of the individual telescopic sections, i.e. in the case of hydraulic actuation to the telescopic cylinder or, if appropriate, also to the piston rod of the hydraulic piston-cylinder system. Separate mechanical drives may be provided in this case. Preferably, however, a common mechanical drive for both locking units is provided. In this case, it is particularly expedient to use a torque-transmission means of variable length, for example a telescopic torque-transmission means (e.g. profiled rods or tubes).
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.